A major problem facing members of the drilling industry has been the necessity of maintaining a straight and true hole. Due to a number of debilitating factors, a drill bit may tend to deviate from the path originally set for it. For example, surface conditions, underlying rock formations and worn-out equipment may contribute to the undesirable problem of drill deviation.
In relatively shallow holes, the angle of deviation is generally not pronounced and oftentimes it may be ignored. However, in deep holes, the deviation may amount to twenty-five degrees or more. Indeed, it has been reported that a hole, initially started in a vertical direction, had deviated seventy degrees at a depth of 1000 feet.
As a consequence to the above, various types of drill stabilizers have been developed to maintain straight line drilling. A common stabilizer is the roller-type stabilizer. Generally, it is annular in shape having a plurality of rollers attached to the periphery of the annulus. These devices are sequentially positioned above the drill bit. The rollers are undersized so that the diameter of the drill bit is slightly larger than the diameter of the rollers to accommodate eventual bit wear. As a result of this design, the rollers exert equal pressure against the walls of the hole as the bit proceeds to drill. The stabilizers act as a stabilizing influence on the bit and they prevent it from wobbling and hunting within the hole. Other examples of stabilizers include friction or drag types and marine bearing types.
Unfortunately, however, the stabilizers presently available do not have the ability to maintain a close contact tolerance with the hole diameter because of the wear and erosion experienced by the rollers. This debilitating wear occurs primarily because as the rollers rotate within the hole above the bit, they are constantly in rotational, frictional contact with the hole wall. This wearing action eventually results in increased tolerances between the rollers and the wall, thus reducing the effectiveness of the stabilizers. This loss of stability in the hole results in increased bit deviation and in additional drilling costs.
Furthermore, as alluded to earlier, in many drilling applications, the stabilizers presently available cannot be used effectively due to the undersizing of the stabilizers in relation to the drill bit. As the bit wears down, eventually the stabilizers will jam against the wall of the hole thereby interfering with the drilling process.
Therefore, a conventional stabilizer must be down-sized initially to accommodate drill wear. Unfortunately, this results in a sloppy fit within the hole, substantially reducing the effectiveness of the stabilizer.